The flight of an aircraft can be modified using flight control surfaces that are connected to the aircraft's wing. The control surfaces include ailerons, flaps, and spoilers that can be used to roll the aircraft, provide additional lift, and/or control airspeed of the aircraft.
An aileron is a hinged panel on the trailing edge of the wing, usually located at the outboard portion of the wing. The aileron can either be raised or lowered to decrease or increase lift on the wing. When deflected downwardly, the aileron increases the lift of the wing, to roll or bank the airplane into a turn. At the same time, the aileron on the other wing is deflected upwardly, to decrease the lift on that wing to augment the rolling motion.
Flaps are surfaces that are mounted at the trailing edge of each wing. During high-speed flight, the flaps are retracted underneath the wing and do not usually contribute to the aerodynamic characteristics of the wing. During low speed flight, however, the flaps can be deployed from the trailing edge of the wing to modify the shape of the wing to increase lift.
Generally, the flaps increase the wing's camber—the degree of asymmetry between the top surface and bottom surface of the wing. Although deployed flaps create drag, the flaps can be used during take-off or landing to increase lift and to allow for flight at slow speed. In some aircraft, the flaps are deployed on a rail or track system that allows the flaps to extend away from the trailing edge of the wing, thereby increasing both the wing's camber and surface area. Generally, flaps cannot be moved and cannot be used as control surfaces to roll or bank the aircraft. Instead, those actions are implemented using ailerons.
One of the most objectionable features of conventional aileron applications is a phenomenon referred to as “adverse yaw.” When a turn is initiated with conventional ailerons, the nose of the airplane turns first in a direction opposite to that of the intended turn. This is usually compensated for by using rudder deflection to coordinate the turn. The adverse yawing motion is a direct result of aileron application. While producing more lift to bank the airplane into a turn, the downwardly-deflected aileron also produces more drag, which acts momentarily to cause the airplane's nose to turn in the direction opposite to the intended turn. That is, when one wing is lifted relative to the other wing by operation of a conventional aileron to bank the airplane into a turn, it is also pulled back away from the turn relative to the wing on the other side, causing the nose initially to turn, or yaw, in the direction opposite to the turn. This effect becomes increasingly detrimental as the roll rate increases and/or airspeed decreases.
In addition to resulting in inefficient flight, adverse yaw produced by the conventional aileron often contributes to spin entry. When spinning, an airplane is descending and turning in a tight spiral flight path. In a left hand spin, for example, the left wing is down and toward the center of the spiral. Instinctively, many pilots are tempted to initiate right stick or control yoke movement to roll towards the right and out of the spin. With conventional ailerons this action deploys the left aileron down and the right aileron up. The left aileron may create more drag and the spin will be further aggravated.
Another disadvantage of conventional ailerons is that they also require commitment of a sizable portion of the trailing edge of the wing that could otherwise be used for beneficial high-lift devices such as flaps that would allow lower approach, landing and takeoff speeds, especially advantageous for heavy, high-speed commercial and high-performance military aircraft. Because, conventional ailerons are moved upwards and downwards, they cannot be placed above conventional flaps which are, generally, incapable of movement. As a result, different regions of the trailing edge of a wing are separately used for either aileron or flap placement.
In view of the draw-backs of conventional aileron and flap configurations, an improved aircraft aileron system has been developed. The improved aileron system is described in U.S. Pat. No. 6,079,672 to Lam, et al. and U.S. Pat. No. 6,554,229 to Lam, et al. and includes two independent panels located at the rear portion of the wing. The panels are located in a span-wise direction and aligned with the wing's trailing edge. The panels are independently hinged at their leading edges and are configured to rotate to create angular deflections with respect to the wing. The upper panel (the “aileron panel”) may be restricted to upward deflection only from its neutral position and in operation is deployed independently as an aileron. The lower panel (the “flap panel”) is capable of both upward and downward deflections from its neutral position, and is deployed independently downward as an auxiliary flap. Both panels are deployed together upwardly only as an aileron. Alternatively, the auxiliary flap panel is capable of downward deployment only, to provide a simpler aileron system. For roll control of an aircraft during cruise, the aileron panel on one side only is deflected up while the aileron panel on the other side remains close-to or in its neutral position.
In both conventional and dual-panel aileron control surface implementations, the ailerons may be configured to deflect upward simultaneously on both wings to act as air brakes. To minimize upward pitch of the aircraft during air braking, the ailerons may be engaged in conjunction with a partial downward deployment of flap panels. By using a controlled deployment of the flap panels during air braking, the pitching moment can be minimized resulting in a controlled slowing of the aircraft.
When using a combination of aileron and flap during air braking, aircraft roll control can be maintained by superimposing differential deflection of the upwardly-deflected aileron panels. For example, during air braking, to bank the aircraft to the right, the angle of deployment of the starboard upwardly-deployed aileron can be increased, while the angle of deployment of the port upwardly-deployed aileron can be decreased. Additionally, the same control logic may allow simultaneous control of the aircraft around the aircraft's vertical or z-axis (i.e., yaw control) by deploying a combination of flap panel and aileron panel of each wing asymmetrically.
For example, to yaw the aircraft during air braking, the deployment of both the aileron and flap panel on one side of the aircraft can be increased, while the deployment of both the aileron and flap panel on the other side of the aircraft can be decreased. Besides providing an additional control mode for conventional aircraft with empennage, this may be highly desirable for aircraft lacking a conventional rudder such as a flying wing.
To control each of the aircraft's control surfaces, a pilot is provided with several flight control mechanisms. The control mechanisms may include levers, wheels, rudder pedals, or yokes and collectively allow a pilot of the aircraft to control a position of each of the control surfaces on the aircraft. When making a turn, for example, a pilot manipulates the ailerons of the aircraft to initiate a bank, while also operating the aircraft's rudder to minimize adverse yaw.
Often, a pilot may provide multiple inputs to a single control surface. For example, if a pilot wishes to implement air braking and bank the aircraft at the same time, the maneuver requires the pilot to manipulate two separate controls—the air brake control and roll control. In order to communicate the pilot's multiple control inputs to the single activated control surface, there is a need for a mechanical control mixer configured to combine multiple control inputs into a single output that is communicated to a single aircraft control surface or combination of control surfaces.